Alloys exhibit different properties from those of individual constituent metal elements. Therefore, newly developed alloys are expected to have properties (for example, catalytic properties) that conventional metals do not have. On the other hand, metal fine particles are expected to have a variety of applications for reasons such as their large specific areas and possibly different properties and structures from those of bulk metals. For these reasons, various alloy fine particles have been studied. For example, a method for producing alloy particles containing silver and rhodium is disclosed (see Non Patent Literature 1).